Stomach tightened?

Leslie • Married and gave birth to a beautiful baby girl 05 July 2017. ❤️
So the weirdest thing happened. I stood up from laying down in bed to go pee for the ten thousandth time, and my stomach tightened, it didn't feel like a cramp it actually just tightened out of nowhere. It still kinda feels tight but I've never felt this before. I'm 16 weeks today. Anyone else felt this? What could it have been?